Stain resistant nylon carpets enjoy significant market acceptance. Stain resistance is typically imparted to nylon by treating the fiber as a solid filament or in a carpet form by the topical application of a chemical finish as described in the following U.S. patents to Monsanto: U.S. Pat. Nos. 4,501,591; 4,592,940; and 4,839,212. The low acid pH necessary to fix this stain resistant finish has the adverse property of greatly altering the shade of the cationic dye which is normally used on this cationic dyeable fiber, precluding its use as a styling factor to obtain multicolor effects in subsequent carpet. However, by using cationic dyeable nylon, which has been previously dyed with acid dyes, in either a solid shade or, preferably, space printed to give multiple short spacings of color, this complication is overcome.
Nylon carpet fiber is generally classified as to type, depending upon its receptivity to acid dyes and basic or cationic dyes. Cationic dyeable nylons contain sufficient SO.sub.3 H groups or COOH groups within the polymer structure, which groups are receptive to cationic or basic dyes to render the fiber dyeable to a cationic dye. Acid dyeable nylons are essentially conventional nylons, such as polyhexamethylene adipamide and polycaprolactam. Acid dyeable nylons vary as to type and are characterized as being weakly dyed with acid dyes, average dyed with acid dyes, or deeply dyed with acid dyes.
Cationic dyeable nylons generally exhibit inherent stain resistant properties, especially to acid-type stains, as compared to other nylon types used for carpet. Cationic dyeable nylons are dyeable with selected cationic dyes, but suffer from poorer lightfastness, especially in light shades, than do comparable shades dyed on acid dyeable nylon using monosulfonated or premetalized acid dyes. This has resulted in the under-utilization of cationic dyeable nylon as a carpet fiber. The fiber's inherently useful properties which otherwise make it attractive as a carpet fiber previously have not been fully realized.
Initial dyeing is accomplished using the space dyeing or intermittent dyeing technique in which the yarn within a given area or space is dyed a particular color, the color and spaces varying throughout the length of the yarn according to random or predetermined orders.
Dyeing carpet yarn is described in U.S. Pat. No. 4,206,735 which relates to a carpet prepared by space dyeing a polyester or polypropylene yarn then tufting the space dyed yarn with another yarn, undyed and having a susceptibility to a dye to which the polyester or polypropylene space dyeing yarn is not susceptible, followed by dyeing the undyed yarn taking care that the selective dyeability of the undyed yarn does not interfere with the previously space dyed yarn. Tak dyeing is used to provide coloration for the nylon tufts and Tak dyeing is explained in U.S. Pat. No. 4,146,362.
Another type of space dyeing is described in U.S. Pat. No. 4,033,717 to Whitaker in which a continuous filament yarn is knit into a prefabric such as a tube or a sock, selectively dyed in a predetermined pattern using various colors, then deknitted, wound onto cones and heated to develop the color. This is also known as a knit/deknit process. When tufted into a carpet, the tufts of the space dyed yarn are arranged randomly or preferably in predetermined blocks or areas.
Research Disclosure 17913 (March 1979) uses the space dyed yarns of the Whitaker patent, combines them with undyed yarns, then overdyes to a different color to provide a carpet having different color combinations. Space dyed yarns may also be prepared using "resist" techniques to treat the fabric to "resist" the type of dye employed, as described in Jilla, U.S. Pat. No. 3,989,453.
Piece dyeing carpets using carpet pile made from two or more different classes of yarns, one yarn being susceptible to one type of dyeing and the other class of yarns susceptible to a different type of dye, is described in U.S. Pat. No. 3,439,999.